1. Field of the Invention
The present invention relates to a rodless cylinder, and more specifically to a seal structure for a rodless cylinder in which an opening of a cylinder tube is sealed by an end cover.
2. Description of the Related Art
A general overview of a conventional seal structure for a rodless cylinder is given in FIG. 7.
As can be seen from FIG. 7, a reciprocating piston 14 is fitted into a cylinder 12 of a rodless cylinder 10, and the cylinder tube 12 has openings on both ends (only an opening on one end side is shown in FIG. 7) blocked by end covers 22 each having a cushion ring 20 in communication with a pressurizing fluid inlet/outlet hole 18. The piston 14 is fitted with a piston packing 16 to seal the leakage of a pressurizing fluid acting upon the piston 14. The piston packing 16 is provided in close contact with the inner circumferential surface of the cylinder tube 12 and a seal belt 24 having its both ends rigidly attached to the end covers 22.
Meanwhile, in the seal structure to seal the opening of the cylinder tube 12 by the end cover 22, a boss portion 22a having a similar shape to the inner circumferential shape of the cylinder tube 12 is projected to the end cover 22, and a seal member 28 is mounted to an outer circumferential groove 26 formed by machining using a lathe for example at the mid position of the outer circumferential surface of the boss portion 22a. 
Note however that in this conventional seal structure for the rodless cylinder 10, the size in the longitudinal direction must be reduced in order to reduce the entire size. Furthermore, the work to form the outer circumferential groove 26 at the boss portion 22a has kept the manufacturing process from being simplified for reducing the manufacturing cost.
It is a general object of the present invention to provide a seal structure for a rodless cylinder which allows the size and manufacturing cost to be reduced by shortening the boss portion of an end cover blocking a cylinder tube and by removing the outer circumferential groove otherwise formed in the boss portion to fit a seal member.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.